A frequency source is a device or system that provides a signal comprising one or more frequencies. For example, a radio frequency (RF)/microwave frequency source may be used to provide a signal at a frequency in the RF/microwave frequency range. In some examples, frequency sources provide a single, fixed frequency signal. However, such fixed frequency signals may have limited utility. A more general frequency source may provide multiple frequencies. The multiple frequencies may be either provided simultaneously as in the case of a noise source or a comb generator or in a selected manner according to a control or programming input of the frequency source.
In particular, frequency sources may be designed to provide one or more of a plurality of frequencies, according to a predetermined programming. Such programmable frequency sources have a wide variety of uses and may be either programmed at a factory prior to use or field programmable. Examples of programmable frequency sources include those employing diodes or transistors as an active element to generate an oscillation that produces a desired frequency in the output signal.
Programming in a programmable frequency source may be provided by an adjustable component (e.g., an adjustable resistor or capacitor), in some examples. However, adjustable components may severely limit the programmability of a frequency source. For example, in many case the adjustable component may only be adjustable during manufacture. In other examples, an external control circuit or system such as a computer controller provides programming. The external control circuit or system may facilitate field programmability. Unfortunately, such external control circuits/systems generally may increase the cost, complexity and overall size of the programmable frequency source while simultaneously decreasing reliability and durability.
Certain examples have other features that are one of in addition to and in lieu of the features illustrated in the above-referenced figures. These and other features are detailed below with reference to the preceding drawings.